Digital watermarking is a technique for embedding additional information to digital data to protect the copyright or integrity of the digital data.
For example, additional information may be embedded to a space between characters, i.e., intercharacter space, as described in any one of the Japanese Patent Laid-Open Publication Nos. H09-186603, 2002-232679, and 2004-023563. If this type of digital watermarking is to be applied, it is desirable to embed the additional information in a manner imperceptible to a human. It is further desirable to embed a large amount of data, as the additional information, to the intercharacter space.